Even though there are a number of birth control methods available, an ever increasing number women are reverting to abortions as birth control alternatives. Without exploring the moral implications of this issue, there is accordingly increased pressure to provide a birth control method that is totally innocuous, and that the majority of women of reproductive age can benefit from without any moral, social or health repercussions. Natural birth control methods fall into this category.
Many attempts have made in the past to provide a practical birth control method based on Ogino's method, more commonly know as the rhythm or calendar method. They have been used in combination with other physiological changes that normally occur before, during or after ovulation cycles for completeness. Many of them use a microcomputer with a number of input measurements of temperature or other bodily fluid changes, and in doing so they have elaborated a series of disciplines that makes them difficult to use.
For example in accordance with U.S. Pat. No. 4,770,186, a combination of saliva and vaginal mucus resistivity measurements are taken starting 5 days after the first day of menstruation and continuing for about 10 or more days. For each of these days and at the same hour the user must introduce into herself a vaginal probe and a salivary probe, take the measurements and either plot them or input them to a microprocessor based instrument. This method has the disadvantage that there must be a high degree of commitment required by the user to follow such a monthly discipline. In addition, the accuracy of the method in detecting ovulation is questionable since the fertile output projected by this method, not counting the days needed before ovulation, must extend for 4 days after ovulation, one may read a limitation on effectivity considering that the female egg has a maximum fertile life of 12 hours.
U.S. Pat. No. 4,465,077 discloses a method using basal body temperature measurements, menstrual cycle history, vaginal mucus change and gynecological disorder entry. Evaluation of inputs are many times subject to user criteria and some times will require lengthy training by a doctor or specialist, thereby increasing the possibility of reading errors. The menstrual cycle history is used to calculate an average figure. This average is not a true representation of the accumulated data but a tendency of it which will be further modified by error factors and other parameters to produce the final output. The method disclosed in this reference is hence quite complex.
U.S. Pat. No. 4,151,831 discloses the use of a combination of temperature measurements with the rhythm method. This reference states that ovulation occurs 14 days prior to menstruation, although researchers have found that ovulation cycle variations of 12 to 16 days are normal.
The above criteria are also applicable to other known techniques. Considering the seriousness of the problem, the prior art discloses only poor or no data protection from change or erasure that may occur by accidental key input or battery removal. It does not account for short measurements of time. For example, if an ovulation had occurred at 11:PM and then if intercourse takes place the morning after, there will be a high risk of pregnancy, but if intercourse takes place in the afternoon, it will be safe, even though both cases are on the same day. The reason for this is that the female egg has a maximum life of 12 hours after ovulation.